bug#61639: 30.0.50; [PATCH] Do not error out on non image file in image-dired

[Manuel Giraud via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Manuel Giraud <manuel@ledu-giraud.fr>
>> Cc: 61639@debbugs.gnu.org
>> Date: Mon, 20 Feb 2023 14:35:42 +0100
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> >> Date: Sun, 19 Feb 2023 21:09:47 +0100
>> >> From:  Manuel Giraud via "Bug reports for GNU Emacs,
>> >>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> >> 
>> >> This patch prevent errors when using image-dired on non image files.
>> >
>> > Why is it better to show a message than to signal an error?  The
>> > former could go unnoticed, especially if some other message is shown
>> > in the echo-area soon enough.
>> 
>> I don't think it is better.  But for some image-dired usage, I do not
>> find it convenient.  Example: you carefully select some images from a
>> dired buffer and hit `C-t d' to see them in image-dired.  But your
>> selection was not correct and one of those file is not an image: you
>> receive an error (and have to correct your selection) and don't get to
>> see any of the correctly selected images.
>
> So maybe "C-t d" should filter the selected "images" before it calls
> the function which errors out?

That is what `image-dired-show-all-from-dir' is doing: it selects files
from the given directory with the correct "image files" regexp and so no
non image will be present.

So your idea is to keep `image-dired--get-create-thumbnail-file' as is
and filter its input in `image-dired-display-thumbs'?  But then we won't
get any message or error that something was not an image (this could go
unnoticed as well ;-)

> IOW, if the application doesn't want an API to fail for reasons
> specific to the application, the onus of avoiding the error is on the
> application, no?

Yes, but maybe `image-dired--get-create-thumbnail-file' is not really an
established API.  It is called twice in Emacs (and the other place it is
called non images are already filtered out).

Do you think it could have been used in third-party package?
-- 
Manuel Giraud